\documentclass{article}
% Preemble
%\usepackage{parskip}
\setcounter{secnumdepth}{1}
\setcounter{tocdepth}{3}
%\setlength{\parskip}{5mm}
\setlength{\parskip}{5mm plus1mm minus2mm}
\setlength{\parindent}{6mm}

\begin{document}
% Top Matter
\title{How to Structure a \LaTeX{} Document}
\author{Andrew Roberts\\
		School of Computing,\\
		Leeds,\\
		United Kingdom,\\
		LS2 1HE\\
		\texttt{andyr@comp.leeds.ac.uk}}
\date{\today}
\maketitle

\begin{abstract}

The abstract goes here...

\end{abstract}

\tableofcontents

% main section

\section*{Introduction}

\addcontentsline{toc}{section}{Introduction}

This section's content...

Paragraph 2...

\section{Structure}

This section's content...

Paragraph 2...

\subsection{Top Matter}

This subsection's content...

Paragraph 2...

\subsubsection{Article Information}

This subsubsection's content...

Paragraph 2...

\appendix

\section{First Appendix}

Appendix one...

\section{Second Appendix}

Appendix two...

\end{document}
